介绍了用光声技术结合调频锁相技术测量薄膜热扩散率的一种新方法，将锁相分析仪用作相关和矢量分析，测试样品在调频范围的光声信号的相位可快速而准确地测出，用计算机对相位数据进行处理即可得到样品的热扩散率，用几十微米厚的钛膜检验了此方法，实验结果表明此方法对测量薄膜热扩散率是非常有效的 A new method of measuring the thermal diffusivity of thin films by photoacoustic technique combined with frequency-modulation phase-locked technique is introduced. The phase-locked analyzer is used as a correlation and vector analysis. The phase of the photoacoustic signal of the test sample in the FM range can be quickly and accurately The thermal diffusivity of the sample can be obtained by processing the phase data with a computer. The method is verified by a tens of micrometer thick titanium film. The experimental results show that this method is very effective in measuring the thermal diffusivity of the film